diff --git a/stringCalculator.py b/stringCalculator.py
index 5532a07f3f46af68cf160bcab7a191728f243e70..3c58954ab30323965ab60131c52cdb39f67f97b2 100644
--- a/stringCalculator.py
+++ b/stringCalculator.py
@@ -41,6 +41,9 @@ class StringCalculator(IStringCalculator):
         result = 0
         for num in list:
             result += int(num.strip())
+            '''Negative Ergebnisse nicht gestatten'''
+            if result < 0:
+                return "negatives not allowed"
 
         return result
         
@@ -77,6 +80,10 @@ class TestStringCalculator(unittest.TestCase):
         res = self.c.add("1\n2,3")
         self.assertEqual(res, 6)
 
+    def test_negativeValues(self):
+        res = self.c.add("-3")
+        self.assertEqual(res, "negatives not allowed")
+
 
 if __name__ == "__main__":
     unittest.main()
\ No newline at end of file